There is proposed a system that controls an automobile to travel a road and provides driving support for a driver of the automobile to travel the road based on a shape of the road to be traveled. The system requires acquiring accurate information about the road shape. For example, accurate information about a curve shape is required when an automobile is going to travel a tight curve and a driver needs to change a vehicle speed as appropriately as possible according to a natural feeling.
A navigation system includes map data as database. The navigation system uses a GPS receiver to detect a position of the traveling vehicle and compares the detected position information with the map data to specify the vehicle position on the map. To generate the map data used for the navigation system, a commercially available road map is used to sample points on a road at regular intervals to extract node points. Two-dimensional coordinate information about the nodes is stored in a storage.
However, presently available maps for car navigation systems aim at route search and route guidance to destinations. These maps are not so accurate as to control the vehicle travel or support the driver in driving.
There are proposed map generation devices to generate map data based on a route the vehicle actually traveled (e.g., see patent literatures 1 and 2).
However, an actual vehicular swept path does not indicate a steady section (a regular-curvature section) existent on a constructed road even if the map generation device according to the prior art is used to generate map data. A steady section length cannot be digitized accurately. A vehicle speed cannot be controlled appropriately in relation to a curve.